Another Quantum of Solstice...

Rutherford and Bohr

[this story continues in part from here.]

Ernest Rutherford discovered the atom's very kernel, the nucleus, but his tiny solar system model of the atom failed. It failed because it had a fatal flaw according to classical electromagnetic theory: Viewed side-on in the plane of the ecliptic, the orbiting electron oscillates charge from side to side and should behave like a miniature transmitter, broadcasting electromagnetic energy like a Marconi transmitter. Giving off energy, bit-by-bit, the electron should spiral into the nucleus. Rutherford never explained that away.

The Importance of Being Near Ernest

Luckily, Rutherford confided his 1909 experiments to young Niels Bohr prior to publishing them. Rutherford had invited Bohr to Manchester to study physics after a brief (and apparently unsuccessful) stint at Cambridge. Inspired,* Bohr spent the summer of 1910 and the subsequent spring (taking time off to marry and to honeymoon), devising his own theory which he published in 1913 (two years after Rutherford finally published his planetary model in 1911).

Bohr got around Rutherford's electron death spiral problem by postulating that it didn't happen! That may sound audacious and even glib, but he overcame "illogical leaps" by solving a bigger mystery which had puzzled generations of scientists: he explained the long-known but little-understood signature hydrogen lines observed in the spectra of stars (recall that stars are mostly hydrogen). According to Bohr, the lines represented quantum leaps in units of energy. He did the math for the hydrogen atom to prove it. The simplistic hope that atoms and the universe were fundamentally similar -- the too small to be seen and the too big to be noticed were whirling masses in motion or "turtles all the way down" -- shone briefly.

According to Bohr's new 1913 theory, electrons encircled a nucleus, but only in stable, fixed-distance orbits (shades of Bode's earlier but discredited planetary law?) but without the continuous death spiral energy radiation. Bohr called his quantized orbits "stationary orbits" (whence my title). A quantum of solstice or standing still.

Electrons in Bohr's stationary orbits still gained or lost energy -- but only by jumping from one orbit to a bigger orbit and vice verse. That was revolutionary. Bohr's math worked out too and depended on Planck's constant which was only 13 years old then.

Planck quantized radiation and Bohr quantized matter--viz, electrons. Scientists struggled in subsequent years with the question of whether electrons were waves or particles and whether light rays were waves or particles. They worried about the meanings of such apparent dichotomies until they gradually realized that they were fighting about language and not about science.
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*Inspired is an understatement

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My inspiration for the "Quantum of Solstice" is here at Victoria's old blog, to whom I dedicate this blog post.

The Vortex is a Downwards Death Spiral

More than 50 years before Rutherford's proof of the positively charged nucleus in 1909 (published in 1911), a physicist named Rankine had notions which today sound downright prescient. He described in 1850:

Each atom of matter consists of a nucleus, or central point, enveloped by an elastic atmosphere which is retained in its position by attractive forces, and that the elasticity due to heat arises from the centrifugal force of these atmospheres, revolving or oscillating about their nuclei or central points. link

There were no plus and minus charges in Rankine's so-called Vortex Theory.  There were no protons and electrons--there was no polarity. Things were held together presumably by gravity.  But the notion of a hard kernel having squishy orbiting clouds is intriguing in retrospect. It's reminiscent of what came later.  Or something.

Then there was Nagaota whose 1904 planetary model for the atom was in part correct.  Just as the planets circled the sun with gravity and momentum in balance...so it was at the atomic level with electrostatic forces and momentum: a tiny negative electron revolved around a positive nucleus. What gravity writ large, electrostatics writ small: electrostatic attraction countered an electron's momentum, keeping things in balance. This had the added appeal of offering a certain symmetry for the outwardly large and the inwardly small: everything was just whirling masses in motion. Turtles all the way down and up. A few remaining fundamental differences between atoms and planets remained, such as the way that electrons always circled in discrete orbits while planets did not (or did they?), but these problems were sure to be solved.  And as wrong as the model proved to be, it stuck with us: